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 A271995 The Pnictogen sequence: a(n) = A018227(n)-3. 2
 7, 15, 33, 51, 83, 115, 165, 215, 287, 359, 457, 555, 683, 811, 973, 1135, 1335, 1535, 1777, 2019, 2307, 2595, 2933, 3271, 3663, 4055, 4505, 4955, 5467, 5979, 6557, 7135, 7783, 8431, 9153, 9875, 10675, 11475, 12357, 13239, 14207, 15175, 16233, 17291, 18443 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Terms up to 115 are the atomic numbers of the elements of group 15 in the periodic table. Those elements are also known as pnictogens. LINKS Colin Barker, Table of n, a(n) for n = 2..1000 Wikipedia, Pnictogen. Index entries for linear recurrences with constant coefficients, signature (2,1,-4,1,2,-1). FORMULA From Colin Barker, Jun 19 2016, corrected Jun 26 2016: (Start) a(n) = (6*(-7+(-1)^n)+(25+3*(-1)^n)*n+12*n^2+2*n^3)/12. a(n) = (n^3+6*n^2+14*n-18)/6 for n even. a(n) = (n^3+6*n^2+11*n-24)/6 for n odd. a(n) = 2*a(n-1)+a(n-2)-4*a(n-3)+a(n-4)+2*a(n-5)-a(n-6) for n>7. G.f.: x^2*(7+x-4*x^2-2*x^3+x^4+x^5) / ((1-x)^4*(1+x)^2). (End) PROG (PARI) Vec(x^2*(7+x-4*x^2-2*x^3+x^4+x^5)/((1-x)^4*(1+x)^2) + O(x^100)) \\ Colin Barker, Jun 19 2016, corrected Jun 26 2016 CROSSREFS Cf. A018227. Sequence in context: A159695 A014001 A291642 * A174792 A063592 A159792 Adjacent sequences:  A271992 A271993 A271994 * A271996 A271997 A271998 KEYWORD nonn,easy AUTHOR Natan Arie Consigli, Jun 18 2016 STATUS approved

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Last modified August 2 02:53 EDT 2021. Contains 346409 sequences. (Running on oeis4.)